If the part is aseptic it shrivels, and presents the ordinary features
of dry gangrene. It is liable, however, especially in the lower
extremity and when the veins also are obstructed, to become infected and
to assume the characters of the moist type.
The extent of the gangrene depends upon the site of impaction of the
embolus, thus if the _abdominal aorta_ becomes suddenly occluded by an
embolus at its bifurcation, the obstruction of the iliacs and femorals
induces symmetrical gangrene of both extremities as high as the inguinal
ligaments. When gangrene follows occlusion of the _external iliac_ or of
the _femoral artery_ above the origin of its deep branch, the death of
the limb extends as high as the middle or upper third of the thigh. When
the _femoral_ below the origin of its deep branch or the _popliteal
artery_ is obstructed, the veins remaining pervious, the anastomosis
through the profunda is sufficient to maintain the vascular supply, and
gangrene does not necessarily follow. The rupture of a popliteal
aneurysm, however, by compressing the vein and the articular branches,
usually determines gangrene. When an embolus becomes impacted at the
_bifurcation of the popliteal_, if gangrene ensues it usually spreads
well up the leg.
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